The present invention relates generally to systems for estimating the mass of a vehicle carrying an internal combustion engine, and more specifically to such systems operable to dynamically estimate vehicle mass based on engine/vehicle operating conditions.
Systems for estimating vehicle mass or weight are known and typically used in medium and heavy duty truck applications wherein such information is useful for optimizing any of a number of engine and/or transmission operating conditions. One particular class of such systems makes use of Newton""s second law of motion by estimating mass in accordance with an equation of the form m=F/A, where m is the mass of the vehicle, F is the vehicle driving force and A is the vehicle acceleration.
Unfortunately, known systems for estimating vehicle mass based on the foregoing equation have a number of drawbacks associated therewith. For example, the vehicle driving force, F, is oftentimes determined in known systems as a rough estimation of the actual driving force of the vehicle that occurs at the vehicle wheels. Many force factors, both additive and resistive, contribute to the actual driving force seen at the vehicle wheels, and the use of inaccurate vehicle driving force values may lead to gross errors in the estimated vehicle mass values.
As another example, known systems for estimating vehicle mass generally fail to optimize conditions under which vehicle driving force and vehicle acceleration data is sampled, resulting in non-linearities and other data measurement inaccuracies. As a specific example, driveline windup effects at the onset of a vehicle acceleration event can contribute to inaccurate driving force and acceleration measurements, although known vehicle mass estimating systems typically do not compensate for such effects. As another specific example, while most known vehicle mass estimating systems require certain operating conditions to be satisfied prior to computing mass estimate values, e.g., vehicle acceleration above an acceleration threshold, transmission gear engaged, etc., such systems generally fall short in providing for optimal operating conditions for computing such estimates.
As yet another example, known systems for estimating vehicle mass are generally operable to compute vehicle mass estimates upon satisfaction of certain operating conditions as just described, but fail to either discontinue computing or disregard such estimates under operating conditions that may grossly corrupt the data. For example, any of a number of typically unaccounted for environmental factors may impart forces, either additive or resistive, on the vehicle that may at the very least corrupt the estimated mass values, and more often render such estimated values highly inaccurate. As a specific example, road grade conditions greater than only a few percent or less, wind conditions, road surface conditions, and the like, can each contribute to vehicle mass estimates that so remote from the true vehicle mass so as to render such estimates unusable.
Unfortunately, known vehicle mass estimating systems typically include such highly inaccurate estimates in their vehicle mass computations, and as a result must employ filtering techniques designed to minimize the impact of such poor estimates on final or running mass estimate values. One popular filtering technique is to maintain as a vehicle mass estimate the running average of several tens, hundreds or thousands of individual vehicle mass estimate values in hopes that this running average will xe2x80x9cabsorbxe2x80x9d poor estimates and more closely reflect the true vehicle mass. However, this approach is generally undesirable, particularly in systems that require a responsive indication of instantaneous vehicle mass changes, such as when an operator either drops or picks up a trailer and/or loads or unloads cargo. With known vehicle mass estimating systems of the type just described, the running vehicle mass average value will generally not provide such a responsive indication of instantaneous mass changes, but will instead provide only a gradual indication over an extended time period.
What is therefore needed is an improved system for estimating vehicle mass that provides accurate vehicle mass information and that is highly responsive to instantaneous changes in actual vehicle mass.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for estimating vehicle mass comprises a speed sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto, means for determining a gear ratio of the transmission, and a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of the vehicle speed signal and estimating a mass of the vehicle as a function of the vehicle driving force and the vehicle acceleration only if the gear ratio is between predefined high and low gear ratio values.
In accordance with another aspect of the present invention, a method of estimating vehicle mass comprises determining a road speed of a vehicle carrying an internal combustion engine coupled to a transmission, determining a gear ratio of the transmission, determining a vehicle driving force, computing a vehicle acceleration value as a function of the road speed, and estimating a mass of the vehicle as a function of the vehicle driving force and the vehicle acceleration value only if the gear ratio is between first and second predefined gear ratio values.
In accordance with yet another aspect of the present invention, a system for estimating vehicle mass comprises a first sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine, a second sensor producing an engine speed signal indicative of rotational speed of the engine, a fuel system responsive to a fueling signal to supply fuel to the engine, and a control circuit producing the fueling signal and computing an engine driving force as a function thereof, the control circuit responsive to the engine speed signal to determine a first resistance force associated with at least one accessory driven by the engine and to compute a net driving force as a function of the engine driving force and the first resistance force, the control circuit determining a vehicle acceleration value as a function of the vehicle speed signal and estimating a mass of the vehicle as a function of the vehicle acceleration value and the net driving force.
In accordance with still another aspect of the present invention, a method of estimating vehicle mass comprises determining a road speed of a vehicle carrying an internal combustion engine, determining a rotational speed of the engine, computing a vehicle acceleration value as a function of the road speed, determining an engine driving force, determining a first resistance force as a function of the rotational speed, the first resistance force corresponding to a force required to overcome a load resistance of at least one accessory driven by the engine, computing a net driving force as a function of the engine driving force and the first resistance force, and estimating a mass of the vehicle as a function of the vehicle acceleration value and the net driving force.
In accordance with a further aspect of the present invention, a system for estimating vehicle mass comprises a speed sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine, and a control circuit responsive to the vehicle speed signal to compute a vehicle acceleration value, the control circuit responsive to the vehicle acceleration value exceeding an acceleration threshold to execute a data collection sequence by periodically computing instantaneous vehicle mass values as functions of instantaneous vehicle driving force and vehicle acceleration value pairs, and to the vehicle acceleration value dropping below the acceleration threshold to terminate the data collection sequence, the control circuit estimating a vehicle mass value as a function of only instantaneous vehicle mass values computed near termination of the data collection sequence.
In accordance with yet a further aspect of the present invention, a method of estimating vehicle mass comprises determining a road speed of a vehicle carrying an internal combustion engine, computing a vehicle acceleration value as a function of the road speed, executing a data collection sequence by periodically computing instantaneous vehicle mass values as functions of instantaneous vehicle driving force and vehicle acceleration pairs if the vehicle acceleration value exceeds a vehicle acceleration threshold, terminating the data collection sequence if the vehicle acceleration value drops below the vehicle acceleration threshold, and estimating a vehicle mass value as a function of only a subset of the instantaneous vehicle mass values computed near termination of the data collection sequence.
In accordance with still a further aspect of the present invention, a system for estimating vehicle mass comprises a sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto, and a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of the vehicle speed signal and computing an instantaneous vehicle mass value as a function of the vehicle driving force and the vehicle acceleration, the control circuit monitoring the vehicle speed signal and the transmission and estimating a vehicle mass value as a function of the instantaneous vehicle mass value only if the road speed changes less than a road speed change amount during a subsequent transmission gear shift.
In accordance with another aspect of the present invention, a method of estimating vehicle mass comprises sensing road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto, determining a vehicle driving force, computing a vehicle acceleration value as a function of the road speed, computing an instantaneous vehicle mass value as a function of the vehicle driving force and the vehicle acceleration value, monitoring the road speed during a gear shift of the transmission subsequent to computing the instantaneous vehicle mass value, and estimating a vehicle mass value as a function of the instantaneous vehicle mass value if the road speed changes less than a road speed change amount during the gear shift.
In accordance with still another aspect of the present invention, a system for estimating vehicle mass comprises a speed sensor producing a vehicle speed signal indicative of a road speed of a vehicle carrying an internal combustion engine, and a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of the vehicle speed signal and estimating a vehicle mass value as a function of the vehicle driving force and the vehicle acceleration, the control circuit combining the vehicle mass value with an existing vehicle mass estimate if a difference therebetween is less than a difference value.
In accordance with still a further aspect of the present invention, a method of estimating vehicle mass comprises sensing a plurality of road speed values of a vehicle carrying an internal combustion engine, computing a corresponding plurality of vehicle acceleration values as functions of the plurality of road speed values, determining a corresponding plurality of vehicle drive force values, estimating a corresponding plurality of vehicle mass values as functions of the plurality of vehicle acceleration and vehicle drive force values, comparing the plurality of vehicle mass values with an existing vehicle mass estimate, and combining the plurality of vehicle mass values with the existing vehicle mass estimate if differences between at least a consecutive number of the plurality of vehicle mass values and the existing vehicle mass estimate are less than a difference value.
One object of the present invention is to provide a system and method for estimating vehicle mass that overcomes drawbacks associated with known vehicle mass estimating systems.
Another object of the present invention is to provide such a system operable to estimate vehicle mass according to the general equation m=F/A, where m is the vehicle mass, F is the vehicle driving force and A is the vehicle acceleration.
Still another object of the present invention is to provide such a system operable to estimate vehicle mass only when certain engine/vehicle operating conditions are met.
Still another object of the present invention is to provide such a system operable to estimate vehicle mass only when an environmental resistance parameter indicative of environmental forces acting on the vehicle (e.g., road grade, wind, etc.), is within prescribed limits.
Yet another object of the present invention is to provide such a system operable to sample vehicle driving force and vehicle acceleration information in a region of vehicle acceleration that minimizes elastic and other driveline effects on such information.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.
FIG. 1 is a diagrammatic illustration of one preferred embodiment of a system for estimating vehicle mass, in accordance with the present invention.
FIG. 2A is a flowchart illustrating one preferred embodiment of a software algorithm for estimating vehicle mass, in accordance with another aspect of the present invention, using the system of FIG. 1.
FIG. 2B is a diagrammatic illustration of a memory register demonstrating one preferred technique for storing instantaneous vehicle mass estimate values, in accordance with the present invention.
FIG. 3 is a flowchart illustrating one preferred embodiment of a software algorithm for determining a net driving force at the wheels of the vehicle for use by the algorithm of FIG. 2.
FIG. 4 is a plot of estimated vehicle mass and gear ratio over time illustrating one preferred technique for collecting net driving force and vehicle acceleration data for use by the algorithm of FIG. 2 in estimating vehicle mass.
FIG. 5 is a flowchart illustrating one preferred embodiment of a software algorithm for determining an environmental resistance parameter, indicative of environmental resistance forces acting on the vehicle, for use by the algorithm of FIG. 2.
FIG. 6 is a plot of vehicle speed, gear ratio and environmental resistance illustrating operation of the algorithm of FIG. 5.
FIG. 7A is a flowchart illustrating one preferred embodiment of a software algorithm for determining a final vehicle mass estimate based on information generated by the algorithm of FIG. 2.
FIG. 7B is a flowchart illustrating an alternate embodiment of a software algorithm for determining a final vehicle mass estimate based oh information generated by the algorithm of FIG. 2.